def split_prefixed(value: str, option_name: str) -> tuple[str, str]:
    if ":" not in value:
        raise ValueError(f"{option_name}: expected a 'prefix:value' string (e.g. 'closure:...'), got: {value!r}")
    prefix, _, rest = value.partition(":")
    return prefix, rest


def pascal_case(snake: str) -> str:
    return "".join(word.capitalize() for word in snake.split("_"))